A nested list is a list that appears as an element in another list. In this
list, the element with index 3 is a nested list.
If we print(nested[3]), we get [10,20]. To extract an element from the
nested list, we can proceed in two steps. First, extract the nested list, then extract the item
of interest. It is also possible to combine those steps using bracket operators that evaluate from
left to right.